a person can drop in the patented modular trigger assembly and attach it to the firearm by two of the firearm’s existing pins. 10. The ‘385 patent fully describes and illustrates a preferred embodiment of the patented modular trigger assembly. That embodiment comprises: a module housing; two hollow modular pins having opposite ends mounted within two pairs of aligned holes in opposing sidewalls of the housing; and the firearm’s trigger group components (e.g., a trigger and a hammer) mounted on the modular pins, inside the housing, for rotation about those modular pins. Upon placing the drop-in trigger between two sidewalls of a lower receiver, two other pins (e.g., the two existing pins mentioned in Paragraph 9 above) are inserted through the following aligned holes: a pair of holes in each of the receiver sidewalls; and the two hollow modular pins.